(a) Field of the Invention
The present invention relates to a manufacturing method of solar cells, in particular to a method of manufacturing solar cell electrodes by a vapor deposition process without requiring any mask lithography or etching process.
(b) Description of the Prior Art
At present, a widely used solar cell is designed with a p/n junction formed near a top side (which is a light receiving surface) of the solar cell, such that an electron stream can be produced when the solar cell absorbs light energy. In a general design of solar cells, a first group of electric contacts 12 are disposed at a top side 11 of a wafer 1, and a second group of electric contacts 13 disposed at a bottom side 14 of the wafer 1 as shown in FIG. 1. In a typical photoelectric module, these solar cells are electrically connected in series to increase voltage, and the connection is generally accomplished by soldering a conduction band from the top side of a certain solar cell to the bottom side of an adjacent solar cell.
In another type of solar cell structure which is called back-contact silicon solar cell structure as shown in FIG. 2, two groups of electric contacts 12, 13 are designed at the bottom side 14 of the wafer 1. Compared with a traditional silicon solar cell, the back-contact silicon solar cell has the following advantages. Firstly, the back-contact cell has higher conversion efficiency, since the loss of a contact shield is reduced or eliminated (because the sunlight reflected from a grating of the contact cannot be converted into electric power). Secondly, the back-contact cell has an electric circuit that can be produced easily, and thus the cost is low, since the two electrode contacts are formed on the same surface. In an example, a photoelectric module and a solar cell circuit adopted by the back-contact cell can be packaged in a single procedure to achieve the effect of saving cost significantly, compared with the present existing ways of assembling photoelectric modules. Finally, the back-contact cell provides a uniform appearance and a better aesthetic effect which is one of the important factors for a certain application such as a photoelectric system of a building and a foldable photoelectric roof of a car, etc.
In a general manufacturing method of a back-contact cell, mask lithography and etching processes are performed to the bottom side of a wafer for several times to form a p+type (boron) area and an n+type (phosphorous) area and electrodes on a back-sided end by screen printing, and the method includes performing the processes such as mask manufacture, exposure, development and etching for several times. Such method not only involves complicated processes, but also incurs a high cost for the mask manufacturing process. Furthermore, the temperature required for a thermal diffusion treatment is approximately equal to 600˜800□ after the screen printing takes place, and such high-temperature process affects the quality of silicon wafer adversely.